The present invention relates to a fixing device preferably made of plastic material for securing any part to a panel by inserting said fixing device into a bore or hole of standard shape formed in said panel, said hole or bore being round, square, rectangular, oval or being provided with notches and the like; the fixing device accommodating substantial thickness variations in the holding panel. Several forms of embodiment of such a fixing device are known; however they have not all of the above characteristics which are more and more required by users.